1. Field of the Invention
The present invention relates to a method and apparatus for providing air at cryogenic temperatures to materials so that they can be processed for various uses.
More specifically, this invention relates to a method and apparatus for reliably and inexpensively producing air at cryogenic temperatures that can be used to embrittle the material of tires or for other embodiments, preserve food or treat emission gases of pollution producing machinery.
Various devices and apparatus for reducing air to cryogenic temperatures to embrittle materials such as synthetic rubber and the like for recycling tires has been expensive to operate and unreliable in operation.
Presently many conventional cryogenic recycling processes and apparatus require the use of liquid nitrogen or solid carbon dioxide to lower the temperature of the material to be recycled to a point where a subsequent impact or cutting produces a powder or granular material. These cryogenic processes are expensive to implement and operate due to the need for a large plant to produce the liquid nitrogen or solid carbon dioxide and the cost of energy required to operate the system. Thus, many of the cryogenic processes are uneconomical in view of the large amount of rubber and polystyrene waste that is currently produced and that has to be pulverized after it is embrittled.
It has been estimated that there are over 250 million scrap tires discarded every year in the United States and over two billion scrap tires which litter the landscape and have been dumped in landfills. These tires are often found in open dumps where they collect rain or run-off water and serve to promote the breeding of mosquitoes, rats, and other pests. The burning of these tires which in earlier years was permitted, has caused an enormous air pollution due to the noxious gases produced during combustion. By burying these tires in landfills, it has been found that the tires migrate to the surface over a period of time and become a hazard. Later prior art methods have included grinding up the tires or shredding them prior to dumping them in landfills. The conventional shredding and granulating equipment requires a great deal of maintenance, is subject to excessive wear, and is unreliable in operation.
Such devices are shown in U.S. Pat. No. 4,726,530 to Miller Miller uses the conventional shredding granulating and separating devices to produce a granular rubber that can be used either as a supplementary fuel when mixed with coal or in road building when mixed with asphalt paving material.
Tires which cost the motorist between $1.00 and $3.00 a piece to dispose of can now be recycled when granulated into a crumb type rubber for use as a supplementary material in fuel or in road building, and be sold at over $100.00 per ton for these uses. This provides an incentive for any recycling business to be able to convert large numbers of tires into a crumb-type rubber form that can be utilized for these end purposes, and sold at a profit. This will also provide an incentive to eliminate the dumping of tires at landfills and to have the crumb-type or granular rubber recycled to be used as either a fuel supplement or as a paving material. The Miller U.S. Pat. No. 4,726,530 describes the advantages of using granulated rubber as both a supplementary material for fuel and as an additive to asphalt, both uses which can more than accommodate the large number of tires that have to be recycled each year.
2. The Prior Art
The prior art methods for the disposal and/or recycling of scrap or discarded tires are exemplified by U.S. Pat. No. 4,142,688 issued Mar. 6, 1979; U.S. Pat. No. 4,180,004 issued Dec. 25, 1979 to A. O. Johnson; U.S. Pat. No. 4,726,530 issued Jul. 19, 1988 to N. P. Horton; U.S. Pat. No. 4,839,151 issued Jun. 13, 1989 to R. L. Barclay; U.S. Pat. No. 5,057,905 issued Oct. 15, 1991 to F. Apffel; U.S. Pat. No. 5,097,905 issued Mar. 10, 1992 to K. N. Murray; U.S. Pat. No. 5,115,983 issued May 26, 1992 to D. Rutherford, Sr.; and U.S. Pat. No. 5,492,657 issued Feb. 20, 1996 to Danschikov. In addition, efforts were also being made in other countries to address the pollution problem caused by scrap tires. Certain patents also describe cryogenic processes which are expensive to implement such as the patent to Richardson, U.S. Pat. No. 3,718,284, and Hollely, U.S. Pat. No. 4,273,294. Others have attempted to use different chemicals or spray washers, such as U.S. Pat. No. 5,492,657 which used ozone (O3), U.S. Pat. No. 4,607,796 using compression of the rubber at cooler temperatures, U.S. Pat. No. 5,238,194 using an excessive flow of water through an open set of non-rotating grinding stones to produce the rubber particles, U.S. Pat. No. 5,115,983 which after shredding the tire, uses high pressure water jets to separate the shredded rubber from the cording and beading material of the tire, or U.S. Pat. No. 4,625,922, which uses elevated temperatures for comminution of the vulcanized rubber.
It is an object of the present invention to provide a method and apparatus for quickly lowering the temperature of rubber, polystyrene materials, or other materials which can include food stubs to cryogenic levels without the use of liquid nitrogen or any other chemical aids in a series of cooling steps whereby ambient air is cooled through several compression stages to xe2x88x9220xc2x0 C. to xe2x88x92175xc2x0 C. to allow the materials such as rubber to become brittle and thus easily pulverized for use as a fuel or additive. The method and apparatus of the invention take ambient air and compress it using either rotary screw compressors or any conventional compressor to a first compressive level of between 80-90 psia. Any oil resulting from the compression is then removed, and the air is cooled back to 107xc2x0 F. through integral aftercoolers such as air or water coolers following its compression. This cooled air is then fed to a booster compressor powered by a turbo expander where the pressure of the air is boosted to over 180 psia. The air is then cooled by an air cooled aftercooler back to 100xc2x0 F. to 110xc2x0 F., and condensed water is removed in a water separator. The air is then further cooled to approximately 40xc2x0 F. in a chiller using a typical freon refrigeration unit. Condensed water is then removed by an integral water separator attached to the evaporator. Heat is discharged to the atmosphere through a condenser, and the cool compressed air is further dried, and any carbon dioxide is removed in an absorption bed. The dried and purged air is then fed to an expansion turbine, where it cools down to approximately xe2x88x92150xc2x0 F., and is then fed into the bottom portion of a vertical chamber.
If rubber tire chips are fed into the top portion of the chamber, then as the chips move downward through the vertical chamber, the air cooled to a temperature of about xe2x88x92150xc2x0 F. passes upwardly through the chamber, and embrittle the rubber chips. At the bottom portion of the chamber, where the chips have been cooled to embrittled temperatures, they are then fed through an airlock chamber into a hammermill where the embrittled chips can be shattered and ground to the right consistency for the end user. The invention has the advantage that in the vertical chamber where the rubber chips are processed, the chips move downward against the counter current of cool air moving upward so that the coolest air is applied to the chips at the lower end of the chamber just before they are removed by the airlock connected to the hammermill. The cool air thus moving upward against the downwardly moving chips, continuously cools the chips to lower and lower temperatures until the chips reach an embrittlement temperatures at the bottom of the chamber. This system is very efficient and economical to operate and allows for a continuous flow of rubber chips to be processed without interruption.
It is therefore an object according to the present invention to provide an improved method and apparatus for cryogenically cooling chips in a continuous manner using super cooled air against a counter current movement of chips.
It is another object according to the invention to provide an air cooled cryogenic method and apparatus for cooling rubber chips or other materials that is simple in design, reliable in operation, and inexpensive in cost of operation.